As part of an exploratory study, researchers assessed the validity of a system of measuring the distribution of pressure at the body-seat interface to estimate the dynamic behaviour and coupling effects of a person sitting on an elastic seat exposed to vertical vibration. The experimental testing was done on one rigid seat and three elastic seats: a polyurethane foam pad, a soft, contoured car seat and an inflatable air-bubble cushion.
The researchers first successfully tested the system without vibration on 11 subjects seated with or without back support. Then, with a vibration simulator, they subjected 31 men and 27 women individually to three levels of vibration, in the 0.5 to 20 Hz range, on the four types of seats, taking into consideration the subjects' anthropometric dimensions. While examining the validity of the system, the researchers also conducted three series of experiments to determine the biodynamic responses of the human body using a force plate and a pressure-mapping sensor. Results showed that this pressure measurement system is complex in many respects, but can be used effectively to estimate the biodynamic response of human subjects sitting on elastic seats. It was found that the response to vibration of a human subject seated on an elastic seat differs significantly from the response for a rigid seat. “This outcome is due to a coupling effect between the human body and the elastic seat that not only alters the nature of the vibrations transmitted to the seated body, but also considerably changes the body-seat contact area, seated posture and the distribution of the body's weight on the seat. This suggests that the body's response to vibrations depends on the rigidity and damping properties of the seat, and that the body probably absorbs less vibrational energy with seats providing good damping,” said Pierre Marcotte, a researcher at the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST).
The results showed that the seat with the flat polyurethane foam block had superior damping properties to the other models. In addition, by comparing the data for men and women and taking into account differences in body mass, the researchers established effects associated with the sex of the subjects indicating that men and women do not absorb vibrations in the same way.
Albeit exploratory, the study produced target values that could be used in the design of seats and anthropodynamic manikins.
The study is available for free download at http://www.irsst.qc.ca/en/publications-tools/publication/i/100836/n/seated-body-mass-coupled-elastic-seats-vertical-vibration. To find out more about IRSST research projects, follow us on Twitter, Facebook, LinkedIn or YouTube.
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Jacques Millette
Public Affairs Officer
IRSST